1. Field of the Invention
The present invention relates to water-permeable solid materials used as paving materials for parks, recreation trails, roadways, parking lots, and the like.
2. Description of the Related Art
Recently, paving materials having water-permeable properties have drawn attention in view of the requirements for environmental conservation, and various types of paving materials are used in practice.
For example, a method for manufacturing water-permeable concrete is disclosed in Japanese Unexamined Patent Application Publication No. 10-194818 in which cement and water in a ratio of 1 to 0.25 is mixed, and the mixture thus formed is compounded with crushed rock of grade 7 (5 to 2.5 mm) and of grade 6 (13 to 5 mm), a binder, and a pigment, and the compound thus formed is caste on an area to be paved or is cured in a mold so as to yield water-permeable concrete.
However, in the method described above, since crushed rock is primarily used, the material cost is increased. In addition, since crushed rock does not always have the pozzolana property in which curing is performed in the presence of an alkaline material, the amount of cement added is larger compared to the case in which coal ash is used. As a result, the voids in the material are decreased, and hence, the water-permeable properties thereof are also degraded.
A method is disclosed in Japanese Unexamined Patent Application Publication No. 8-239281 in which pyroclast, 300 to 400 kg of cement to 1 m3 of pyroclast (volcanic sand, volcanic ash, or volcanic rock), 0.005 to 0.1 part by weight of a binder which is generally used for mortar, and 0.3 to 0.4 part by weight of water, with respect to 1 part by weight of cement, are compounded, and the compound thus formed is cast on an area to be paved or is cured with pressure in a mold so as to yield water-permeable concrete.
In the method described above, since pyroclast (volcanic sand, volcanic ash, or volcanic rock) is primarily used, the material cost is reduced. However, it is believed that the binder used in the method was not appropriately selected, and as a result, satisfactory strength could not be obtained while ensuring the voids required for high water-permeable properties.
In addition, Japanese Unexamined Patent Application Publication No. 4-198049 discloses a water-permeable composition having an aggregate composed of finely powdered water cooled slag and at least one of crystallized slag, limestone, and water cooled slag, and 1 to 14 percent by weight of an alkaline agent such as cement or gypsum. In the composition described above, a binder is not contained.
In the method described above, cement, gypsum, or the like is used as an alkaline agent which is used for binding the aggregate. Accordingly, the solidification is performed only by the reaction of the alkaline agent mentioned above, and as a result, a composition having water-permeable properties together with strength cannot be obtained.
Recently, the large amount of coal ash generated from thermal power plants and the like has been increasing; in particular, so-called xe2x80x9cclinker ashxe2x80x9d generated at the bottoms of boilers is increasing since appropriate disposal methods therefor have not been developed, and hence, the promotion of effective use of the coal ash is progressively required. In response to the requirements mentioned above, a method for using coal ash, which is generated in large amounts, for water-permeable paving materials as described above is disclosed in Japanese Unexamined Patent Application Publication No. 2-271952. In the method mentioned above, 100 parts by weight of white cement, 100 to 500 parts by weight of coal ash clinker, and 10 to 20 parts by weight of a cement curing agent are mixed, water is then added to the mixture thus formed, and subsequently, the mixture is molded and dried by a roller compacting method so as to form products for civil engineering purposes.
However, in the products for civil engineering purposes formed in accordance with the method disclosed in Japanese Unexamined Patent Application Publication No. 2-271952, the solidification is performed only by the reaction of the cement, and the pozzolana property of the coal ash is not effectively exploited. In addition, since a large amount of cement is used in order to ensure strength, even though it is not clear since the particular water-permeability thereof is not described, it is believed that the voids formed in the material are decreased and that the water-permeability is low.
Accordingly, an object of the present invention is to provide a water-permeable solid material having sufficient water-permeable properties together with sufficient strength for use in paving materials by effective use of so-called xe2x80x9cclinker ashxe2x80x9d generated from thermal power plants and the like. In addition, in order to minimize abrasions when pedestrians fall in the case in which a solid material is used as a paving material, another object of the present invention is to provide a water-permeable solid material in which the surface thereof is flat and small surface irregularities are reduced to be as small as possible.
In order to solve the problems described above, by intensive research by the inventors of the present invention, it was discovered that when clinker ash was used as an aggregate, the particles of the clinker ash could be bound with each other by a small amount of cement using the pozzolana property of the clinker ash. In addition, it was also discovered that when an inorganic material was interposed between the particles of the clinker ash used as the aggregate, the strength was not degraded even if the amount of cement is reduced. Accordingly, it was discovered that a water-permeable solid material could be formed having a predetermined water-permeable properties together with a predetermined strength while voids formed between particles of the clinker ash could be ensured, whereby the present invention was made.
That is, a water-permeable solid material of the present invention is produced by a process comprising the steps of preparing a mixture primarily composed of 9 to 30 parts by weight of cement and 2 to 7 parts by weight of an inorganic additive with respect to 100 parts by weight of clinker ash, compounding the mixture with water, and curing the mixture compounded with water.
When the water-permeable solid material has the composition described above, even though the amount of the cement is small, the particles of the clinker ash can be tightly bound with each other by using the pozzolana property of the clinker ash. The particles of the clinker ash are bound with each other at contacting points therebetween by the cement, the additive intrudes into some of the voids formed by the particles of the clinker ash, and the additive and the cement cross-link the particles of the clinker ash, whereby a bound state of the clinker ash can be obtained. As a result, compared to the case in which only clinker ash is used, the contacting points between particles of the clinker ash are increased by the additive intruded therebetween, and the particles of the clinker ash are tightly bound with each other compared to the case in which the additive is not used. In addition, a high strength can be obtained while the voids formed by the particles of the clinker ash are ensured. In the composition described above, 9 to 30 parts by weight of cement and 2 to 7 parts by weight of an additive with respect to 100 parts by weight of clinker ash mean that there are 9 to 30 g of cement and 2 to 7 g of an additive with respect to 100 g of clinker ash.